Observation of polytype stability in different-impurities-doped 6H–SiC crystals

The Al–B co-doped 6H–SiC and heavily N-doped 6H–SiC crystals grown by physical vapor transport method were investigated in this paper, respectively. The XPS (x-ray photoelectron spectroscope), Raman spectra analysis and XRD (X-ray diffraction) were applied to characterize the obtained SiC crystals. When the co-doping level with a ratio of B:Al = 0.22at.%:0.34at.% was obtained, Raman spectra results showed that there existed the 15R-polytype inclusion in the 6H–SiC crystal. When the co-doping ratio of B and Al increased to 1.18at.%:0.34at.%, there was only one polytype (6H) in the whole wafer. It can be speculated that the co-doping ratio of B:Al = 1.18at.%:0.34at.% may stabilize the crystal structure during the 6H–SiC crystal growth process. But the real mechanism of the polytype stability is unclear. The role of Al or B or other impurities to influence polytype stability will be further investigated in the future work. Moreover, it has been found that a high nitrogen doping level can influence the polytype stability during the 6H–SiC crystal growth process. And especially, the 4H-polytype is preferred.

Research Highlights
► 15R-polytype inclusion existed in the 6H-SiC crystal when B:Al=0.22at%:0.34at%.
► B:Al=1.18at%:0.34at% may stabilize crystal structure during 6H-SiC crystal growth.
► 4H-polytype is preferred in heavily nitrogen-doped 6H-SiC crystals.